Why wasn’t suspect in Houston police sergeant’s murder already behind bars?

There's a lot of questions about why Elmer Manzano wasn't arrested two days ago when police first responded to a domestic abuse call at the Holly Hall Apartment.

Manzano is accused of shooting and killing a Houston police sergeant and injuring a police officer on Tuesday.

HPD sergeant killed, officer injured in southwest Houston shooting

Houston Police Chief Art Acevedo says Sgt. Harold Preston, a 41-year veteran of the department, died in a shooting Tuesday morning.

This past Saturday, Manzano's estranged wife went to a police substation to file a report about her ex. On Sunday, officers were called to the apartment.

According to the District Attorney's office, Officer Courtney Waller, who was shot on Tuesday, said he didn't believe a crime had occurred. So the DA's office decided not to file charges against Manzano.

Manzano is in the country illegally, and even though he's a convicted felon, enough time has passed that would allow him by state law to have a gun at his home.

DETAILS: HPD sergeant killed, officer injured in southwest Houston shooting

Police apparently saw no gun when they were at the apartment on Sunday.

The DA's office says Officer Waller called them again on Tuesday morning before the deadly shoot out took place.

An Assistant DA told him they would accept terroristic threat charges if he thinks a crime occurred. But once again, the DA's office says Officer Waller's response was he didn't believe a crime had occurred.

All of this is now under investigation.

Immigration and Customs Enforcement released the following statement on Manzano:

Elmer Rolando Manzano-Martinez, 51, is a citizen of El Salvador and convicted criminal alien who is unlawfully present in the U.S. On Oct. 20, officers from U.S. Immigration and Customs Enforcement’s (ICE) Enforcement and Removal Operations (ERO) in Houston, Texas, placed an immigration detainer with the Harris County (Texas) Sheriff’s Office (HCSO) on Manzano-Martinez after he was arrested for murder.