(CNN) — Four children were killed as they slept during a 21-hour standoff between police and a gunman who barricaded himself in an Orlando apartment last week.

Officers found the children — ages 1, 6, 10 and 12 — dead once the standoff was over and they entered the apartment.

Gary Lindsey Jr. was also dead of an apparent self-inflicted gunshot wound, police said.

Officers initially responded to the apartment in response domestic violence call from Lindsey’s girlfriend, who had left the apartment.

Lindsey, 35, shot at officers when they arrived, hitting one, said Orlando Police Chief John Mina. At least one officer returned fire, but Mina said he did not know whether Lindsey was hit.

Police said on Twitter Thursday that a preliminary investigation showed the children were found dead while lying in their beds wearing the same “bedtime clothes” their mother said they were in when she put them to bed.

“OPD Homicide Detectives believe the children were killed while they slept, either shortly before or shortly after the suspect’s initial contact with OPD officers,” police said in a statement. Their findings were based on “the condition of the victims’ bodies at the time of discovery, coupled with a thorough review of the investigation so far regarding this case.”

Mina said two children are believed to be Lindsey’s and two are his girlfriend’s.

Lindsey inherited the guns he used — two rifles, two shotguns and a handgun — from his father, Mina said.

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