According to the federal indictment, Alcala would take women's phones during traffic stops in order to confirm their insurance coverage or vehicle registration.
But Alcala searched their phones for nude images and took photos on his own personal phone, the indictment said.
In one case, Alcala allegedly texted himself a video and deleted evidence of the text.
The Missouri Department of Public Safety told NBC News that records show McKnight surrendered his state peace officer license, "which means he can never work as a Missouri law enforcement officer again."
Ashley Johnson, special-agent-in-charge of the FBI St. Louis Division, told people not to hesitate to report uncomfortable encounters with officers.
Persons:
Julian Alcala, Alcala, texted, Jane Doe, He's, Bevis Schock, Schock, David McKnight, McKnight, Ashley Johnson, Louis Division, Johnson
Organizations:
U.S, Attorney, Eastern, of Missouri, U.S . Constitution, Florissant Police, NBC News, FBI, Alcala, Wednesday, Patrol, Attorney's, Missouri, Highway Patrol, The Missouri Department of Public Safety, Louis
Locations:
Missouri, Florissant, U.S .