A manhunt was underway across Texas on Monday for the unidentified man who fatally shot a San Antonio police officer Sunday, a bloody day for police officers across the nation.

Elsewhere Sunday, three police officers were wounded and two suspects killed in shootings in St. Louis and Gladstone, MO, and Sanibel, FL.

In San Antonio, Police Chief William McManus said the murder of Detective Benjamin Marconi during a traffic stop near the police station was more than a random act.

"I feel we (police) were targeted," McManus said. "I think the uniform was the target."

James Pasco, executive director of the National Fraternal Order of Police, said four attacks on officers in one day is another alarming sign of the times. In July, five officers were killed in Dallas by a heavily armed sniper who opened fire at a peaceful protest against police-involved shootings. In Baton Rouge less than two weeks later, three officers were killed and three others wounded in an ambush.​​

Sunday's violence, however, involved four attacks by four attackers scattered across the nation.

Pasco says that, while no direct connection linking Sunday's shootings is apparent, social media spreads information — often incorrect information — quickly and widely and can provoke action. Pasco says a drumbeat of criticism from the media, politicians and activists has eroded the esteem granted to law enforcement from the public.

"Police officers are doing their jobs the best they can, sometimes heroically, but now more than ever this kind of violence is in the back of their minds," Pasco told USA TODAY. "And when cops aren't safe, nobody is safe."