COLUMBIA, S.C. (AP) — Police charged two men with murder Wednesday after a 7-year-old boy was killed 18 months ago when shots were fired into his South Carolina home.

Investigators received almost no tips to solve Knowledge Sims’ death and police used dozens of interviews, ballistic evidence and dogged police work to crack the case, Columbia Police Chief Skip Holbrook said at a news conference.

“This tugged at the heartstrings of every single person in this building from the very beginning,” said Holbrook, his voice breaking a little with emotion. “This case has lingered because we have not had cooperation. We’re better than this.”

Travon Wilson, 24, and Kwatez Carter, 21, both face numerous charges, including murder. Wilson was arrested just before Holbrook’s Wednesday night news conference. Carter is in jail on other charges, including attempted murder, in connection with an unrelated shooting, officials said in a news release. Police didn’t say if either suspect had an attorney who could comment.

Knowledge Sims was killed in April 2020 when someone fired shots into a home with two adults and seven children inside. His 13-year-old sister was wounded and survived, investigators said.

Police have previously said since the boy was not a target. Holbrook repeated that point and said investigators think they know why the gunmen fired on the home, but wouldn’t make it public.

The arrests didn’t happen because of any single development, but were 18 months of work, including matching bullets and casings found at the scene to the guns that were found to have fired them, Holbrook said.

“We had no tips. We relied on the officers beating the street and conducting dozens and dozens of interviews leveraging technology, allowing the forensic examinations to run their course,” the police chief said.