The night manager of a Drury Inn in St. Louis was shot to death during an early Thursday robbery attempt, one of the city's six homicides during a 12-hour span. Police quickly made three arrests in cases in which the victims reportedly knew their assailants.

Police Chief Sam Dotson and Mayor Francis Slay condemned the violence at a Thursday afternoon news conference. They did not identify the suspects in custody, who will be formally charged Friday.

Scott Knopfel, 50, was shot in the head at the Drury hotel near Interstate 44 just before 3 a.m. after he struggled with his assailant while opening a cash drawer. Surveillance video shows the suspect, whom the manager mistook for a patron, entering the hotel and leaving less than 30 seconds later. He can be seen pulling out a handgun and vaulting a counter, then leaving the hotel in the same manner.

Six homicides within 12 hours in an unusually high number for St. Louis, which has a population of about 320,000 people and recorded 159 homicides in 2014. Dotson and Slay linked the overnight violence to crime increases in the area documented since the fatal Ferguson police shooting of 18-year-old Michael Brown more than five months ago in north St. Louis County.

"To see this much violence going on in our city within such a short period of time, it is absolutely outrageous," Slay said. "It's out of hand. It disgusts me."

The first fatal shooting happened about 7:30 p.m. Wednesday during a home invasion near Fountain Park. The city's medical examiner's office identified Leon Rivers, 34, as the victim, who was shot as he ran from the home. A 29-year-old man is in custody.

Shortly after midnight, a man was found shot in the hallway of an apartment complex in the Carondelet neighborhood. Police say Kenny Burgett, 19, was confronted by his girlfriend's former boyfriend. The 22-year-old suspect challenged Burgett to a fist fight before shooting him, according to police.

Just eight minutes later, two men died after a shooting and robbery on a street in the Dutchtown neighborhood. The victims were identified as Eric Lee, 21, and Jerivon Taylor, 20.

A sixth homicide was reported around 8 a.m. Thursday, when Cheri Simpson, 32, was shot to death in her car just south of downtown St. Louis while waiting at a stoplight. Capt. Michael Sack said police have arrested the woman's ex-boyfriend.

Dotson and Slay reiterated the need for more police officers in the city, amplifying calls for 160 new officers over two years in a plan that officials unveiled late last year, and lashed out at what they called light sentences handed down by judges in gun crimes.

"These acts of violence are intolerable," said Dotson. "We cannot allow this in our community. Officers are taking it personally."

___

Follow Alan Scher Zagier on Twitter at http://twitter.com/azagier