A gunman who barricaded himself in an apartment after taking four children hostage shot and killed them all before shooting himself.
Gary Lindsey, 35, was found dead along with children aged one, six, 10 and 11.
He was the father of two of them while the other two were his girlfriend's from a previous relationship.
The bodies were discovered when police stormed the apartment in Orlando, Florida, at about 9pm on Monday after a 21-hour standoff.
City of Orlando police chief John Mina said officers had been communicating with Lindsey to try to reach a peaceful solution, but he had a poor phone connection.
When officers tried to get Lindsey another phone to continue negotiations, they saw at least one child had been shot and decided to storm the apartment.
Mr Mina said: "The situation has a tragic and sad ending. We realise it's been a difficult day for the entire community."
The standoff began on Sunday night, shortly after Lindsey's girlfriend contacted police saying he had assaulted her.
Officers met her outside and she directed them towards an apartment.
Shortly afterwards Lindsey fired a shot that critically wounded an officer at about 11.45pm.
The officer suffered a "very serious and significant injury," when he was shot in the eye and has undergone surgery.
He remained in a critical condition although his injuries are not thought to be life-threatening.
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Mr Mina added: "We've been through this before. It's very hard. It's very traumatic to have one of your officers shot in the line of duty. We're just praying that he's going to be okay."
Lindsey had previously been arrested on domestic violence and arson charges and was on probation.