Man allegedly kills his girlfriend, her 3 kids in 'senseless' mass shooting

A man allegedly killed his girlfriend and her three children in a "senseless" mass shooting in a Florida apartment, according to authorities.

On Tuesday night, after family members called 911, officers responded to the Sunrise Apartments in Lake Wales and found a mother, her son and two daughters shot dead, police said.

The victims were ages 40, 21, 17 and 11, according to police.

Al Stenson allegedly shot them in the apartment around 5 a.m. Tuesday and then fled, according to police.

The motive is unknown, police said.

"Completely senseless. It makes absolutely no sense," Lake Wales Police Chief Chris Velasquez said at a news conference.

When authorities tracked the 38-year-old Stenson to the Slumberland Motel in Sanford, "Stenson made statements that he would kill himself or force law enforcement to kill him," police said in a statement.

An hourslong standoff and negotiations ended with an officer-involved shooting, police said.

He was "going" for a gun on the ground when four officers opened fire, "neutralizing the threat," authorities said at a news conference.

Stenson was pronounced dead at the scene, police said.

ABC News' Robinson Perez contributed to this report.