They then walked to the windows facing the outside staircase, where they’d come from just minutes ago. Noticing police evacuating students, Harris said, "Let's go kill some cops," and they began to shoot out the windows. Police returned fire. After a few seconds, Klebold turned away from the windows and fired his shotgun at a nearby table, injuring Patrick Ireland, Daniel Steepleton, and Makai Hall. He immediately removed his trench coat. Harris grabbed his shotgun and walked over to the lower row of computer desks, firing his gun underneath the first desk in the row without looking to see who was under it. The shot killed Steven Curnow, who was hiding underneath. He then shot under the next computer desk, injuring Kacey Ruegsegger.
Harris walked over to the table across from the lower computer row, slapped the top twice with his hand, knelt down, and said "peek-a-boo," before shooting Cassie Bernall in the head. The recoil from the weapon hit his face, breaking his nose. Although one witness reported that Bernall was the individual who was asked, "Do you believe in God?" the exchange actually happened with Klebold and surviving student Valeen Schnurr. Three students witnessed Bernall's death, including the person who was hiding under the table with her, and testified that Klebold and Bernall did not exchange words. Although some students who were in the library asserted the exchange occurred, none of them physically witnessed it. They may instead have heard the exchange between Klebold and Schnurr and have been misled by news reports that attributed the words to Bernall.
Harris turned to the next table where student Bree Pasquale sat next to the table rather than beneath it. She had not hidden underneath, as there was not enough room. Harris asked her if she wanted to die, and Pasquale responded with a plea for her life. Witnesses report that Harris seemed disoriented, possibly from the wound to his face, which was bleeding heavily. As Harris taunted Pasquale, Patrick Ireland tried to aid Makai Hall, who had suffered a wound to his knee. While doing so, his head came above the table. Klebold shot him, hitting him twice in the head and once in the foot. He was knocked unconscious, but survived.
Klebold then proceeded towards another set of tables, discovering Isaiah Shoels, Matthew Kechter, and Craig Scott, Rachel Scott's brother, hiding under the table. All were popular athletes at the school. Klebold attempted to pull Isaiah out from underneath the table, but was unsuccessful. He then called to Harris, who left Bree Pasquale and joined him. Klebold and Harris taunted Shoels for a few seconds and made derogatory racial comments towards him before Harris knelt down and shot him in the chest at close range, killing him. Klebold also knelt down and opened fire, hitting and killing Matthew Kechter. Craig Scott remained uninjured but he lay in the blood of his friends, pretending to be dead.
Harris turned and threw a CO2 bomb at the table where Hall, Steepleton, and Ireland were located. The CO2 bomb landed on Daniel Steepleton's thigh, but Makai Hall grabbed the bomb and threw it south, away from the shooters.
Harris walked to the bookcases between the west and center section of tables in the library. He jumped on one of the bookcases and shook it, then shot at something in that general area. It is not known what he shot at, since no one could see him at the time. Klebold walked through the main area, past the first set of bookcases, the central desk area, and a second set of bookcases, into the east area. Harris met up with him there. Klebold shot out a display case next to the door, turned, and shot at the closest table to him, injuring Mark Kintgen. He turned to the table to his left and shot at it, injuring Lisa Kreutz and Val Schnurr with the same bullet. He approached the table and fired again, killing Lauren Townsend.
Meanwhile, Harris went over to another table where two girls were hiding, bent down to look at them, and dismissed them as ‘pathetic.’ The shooters then went over to an empty table and reloaded their weapons. Schnurr, who had been hurt badly, began to cry out at that point, "Oh, God help me!" Klebold went back to her and asked her if she believed in God. She floundered in her answer, saying no and then yes, trying to get the answer right. He asked her why and she said it was because it was what her family believed. He taunted her, reloaded his shotgun, and then walked away. The slightly injured Evan Todd reported that Klebold said, "God is gay."
Harris moved to another table and shot twice underneath it, injuring Nicole Nowlen and John Tomlin. When Tomlin tried to crawl out, Klebold came back around the corner and kicked him. Harris taunted his attempt at escape, and Klebold shot him repeatedly, killing him. Harris walked back over to the other side of the table where Lauren Townsend lay. Behind it, Kelly Fleming, like Bree Pasquale, sat next to the table rather than beneath it. Harris shot her with his shotgun, hitting her in the back, killing her instantly. He continued to shoot at the table behind her, hitting Townsend and Kreutz again, and wounding Jeanna Park. An autopsy later revealed that Townsend had been killed by the first shot.
At 11:37 a.m., the shooters moved to the center of the library where they continued to reload their weapons at a table midway across the room. Harris noticed a student nearby, and asked him to identify himself. The student was John Savage, an acquaintance of Klebold's. Savage asked Klebold what they were doing, to which Klebold replied, "Oh, just killing people." Savage asked if they were going to kill him. Klebold said "What?" because the fire alarms were going off. Savage asked again if they were going to kill him. Klebold hesitated, and then told him to leave the library. Savage fled immediately, and escaped via the library's main entrance.
After Savage was gone, Harris turned and fired his carbine at the table directly north of where they had been, hitting Daniel Mauser in the face at close range, killing him. Both shooters moved south from there and fired randomly under another table, critically injuring Jennifer Doyle and Austin Eubanks, and fatally wounding Corey DePooter. DePooter, the last victim of the massacre, was credited with keeping his friends calm during the ordeal.
At this point, several witnesses heard Harris and Klebold comment on how they no longer found a thrill in shooting their victims. Klebold was quoted as having said, "Maybe we should start knifing people; that might be more fun." They had each brought two knives in case it came down to hand-to-hand combat … or to do what Klebold suggested. Both shooters moved away from the table and headed toward the library's main counter. Harris threw a Molotov cocktail toward the southwestern end of the library as he went, but it failed to explode. He came around the east side of the counter and Klebold joined him from the west, converging near where Evan Todd had moved after the copier incident. The shooters made fun of Todd, who was wearing a hat, which meant that he was a jock. When the shooters wanted to see his face, he lifted the hat up partway, so they could not see it. Klebold asked Todd to give him one reason why he should not kill him, and Todd replied, "I don't want trouble." The shooters continued taunting him and debated killing him, but they eventually walked away.
At this point, Harris's nose was bleeding heavily, which is what may have prompted him to decide to leave the library. Klebold turned and fired a shot into an open library staff break room, hitting a small television. He slammed a chair down on top of the computer terminal that was on the library counter, directly above where Patti Nielson had hidden. The two walked out of the library at 11:42 a.m., ending the massacre.