SAN FRANCISCO (KRON) — Sheriff Ross Mirkarimi held a press conference Friday morning to set the record straight about his office’s release of a Mexican national who was in the U.S. illegally and has now been charged in the killing of a woman at San Francisco’s Pier 14.

Mirkarimi has been under public scrutiny from public officials since the tragic shooting death of 32-year-old Kate Steinle.

Steinle, of San Francisco, was walking along the dock on July 1 at about 6:30 p.m.  with her father and a family friend when she was shot and killed.  Her father had his arm around her the moment the gunman opened fire.

The man accused of the murder, Juan Francisco Lopez Sanchez, 45, had a long criminal history dating back to 1991, as well as several deportations prior to his arrest for murder.

On March 26, Sanchez was placed in the custody of San Francisco sheriff’s department for a 20-year-old warrant from December 1995 saying he failed to appear on two drug charges.

Mirkarimi said that the Immigration and Customs Enforcement department issued a civil detainer, or a request to voluntary extend detainment of a person in custody, for Sanchez. “It is not a legal order to extend an individual’s incarceration,” he said.

“Had ICE sought the requested legal order or warrant, the San Francisco sheriff’s department naturally and will always comply and would have complied if that legal order or warrant would have been presented to us.”

The city’s sanctuary law prohibits city employees from helping federal authorities with immigration investigations or arrests unless required by law or warrant. That said, the ordinance does not prohibit local law enforcement from informing ICE that they’ve arrested someone in the country illegally for a felony offense or who has prior felony convictions.

Since ICE did not provide the sheriff’s office with a warrant or legal request to detain Sanchez, he was legally released on April 15, Mirkarimi said.

However, an ICE spokesperson said that Mirkarimi’s assertion that ICE is required to provide some form of judicial order “reflects a manifest misunderstanding of federal immigration law.”

“There is no such document, nor is there any federal court with the authority to issue one. Neither is there a legal requirement that ICE provide a judicial warrant to law enforcement agencies in order to receive such notifications,” said Virginia Kice, ICE Western Regional Communications Director/Spokesperson.

San Francisco is one of more than 320 municipalities, large and small, throughout the country have stopped complying with immigration detainer requests as the detainers are unconstitutional and have damaged trust in law enforcement, according to Daisy A. Vieyra, spokesperson for the ACLU of Northern California.

“Two federal courts have established that ICE detainers violate the 4th amendment,” Mirkarimi said, “ICE failed to obtain a warrant for (Sanchez’s) deportation.”

San Francisco Mayor Ed Lee is also facing criticism for Sanchez’s release and the city’s sanctuary ordinance. Lee responded earlier this by asking, “could a simple phone call with the sheriff letting them know the release of someone in custody…would have prevented this?”

Mirkarimi went on to blame Lee for “playing politics with public safety.”

“The mayor is throwing his own law under the bus,” Mirkarimi said. “If in fact, that he’s looking for some ambiguity in the law in order to cover his position, then it really defeats the purpose of the law in the first place.”

KRON’s Molly Martinez contributed to this report.