Four children — ages 1, 6, 10, and 11 — are dead after a 20-hour standoff in Orlando, according to multiple media reports. The hostage-taker — Gary Lindsey Jr. — is also dead.

Orlando Police Chief John Mina said during a press conference that officers entered the apartment around 2100 hours on Monday and discovered that all the children held hostage were dead. Mina said two children are believed to be Lindsey's and two are his girlfriend’s.

“We have no idea when those poor children lost their lives, that will all be part of the investigation,” Mina said.

Mina said officers were in contact with Lindsey intermittently throughout the standoff, seeking to bring a peaceful resolution to the situation. Lindsey reportedly had a poor phone connection, and when officers tried to get Lindsey another phone to continue negotiations, they saw at least one child had been shot. That’s when the decision was made to enter the apartment.

The standoff began Sunday night, when Lindsey's girlfriend contacted police to report a domestic violence incident.

Shortly after officers arrived to the Westbrook apartment complex, Lindsey opened fire, critically wounding Officer Kevin Valencia.

Valencia suffered a “very serious and significant injury.” Following surgery, Valencia is listed in critical condition but is expected to survive.

Related: Orlando Officer Shot in Head, Suspect Barricaded with 4 Children

Related: Orlando Officer Shot, 4 Children Held Hostage by Suspect