Two days after a shooter perched on a rooftop opened fire on an Immigration and Customs Enforcement building in Dallas, authorities say they have uncovered a trove of information pointing to a targeted attack on law enforcement while advocates call for more information about the victims to be released.

Three detainees at the facility were shot early on Sept. 24; one was killed and two critically injured, officials said. No ICE agents or other law enforcement officers were injured.

The outcome was an apparent failure of the suspect's intent, which authorities believe was to specifically kill ICE agents and spare any "collateral damage or injury to the detainees," according to Nancy Larson, acting U.S. attorney for the Northern District of Texas.

Officials identified the suspect as 29-year-old Joshua Jahn on Sept. 25, but haven't released the identities of the three detainees shot. Jahn died of a self-inflicted gunshot wound, officials previously said.

Authorities said an unspent shell casing found near Jahn's body had "ANTI-ICE" written on it, and his writings said he hoped to give ICE agents a "real terror."

A small vigil the evening of Sept. 25 called for the release of details and more acknowledgement of the victims of the shooting, who were all detainees.

Here's what we know about the shooting and investigation:

What we know about the victims killed in ICE facility shooting

Officials have not released the names of the detainee killed in the shooting or the two detainees who were critically wounded.

Among the victims of the shooting was a Mexican national who was left "seriously injured," the country’s Ministry of Foreign Affairs said in a statement. Authorities have not revealed the nationalities of the two other victims.

At a Sept. 26 news conference, Joseph Rothrock, special agent in charge of the Dallas FBI field office, declined to provide the identities of the victims, citing an ongoing ICE process to notify family members and consulate officials.

"That process is ongoing so we'll defer to our ICE counterpoints to at some point determine when it's the right time to release that information."

What we know about the targeted ICE field office

The Dallas ICE field office is a two-story brick building on the access road to Interstate 35E about six miles northwest of downtown Dallas.

One of dozens like it around the country, the Dallas field office doubles as a processing center where ICE agents bring in detained migrants for fingerprints and book-in. Top local ICE brass and support staff have offices there; dozens of agents start and end their workdays there.

Local immigration attorney Vinesh Patel said the building is split into a front-facing, public office meant for immigration check-ins and a rear secure area to temporarily hold detainees. Security guards conduct basic metal detector searches at the front, and the rear doors are fenced off in an open-air parking lot. That's where the shooter fired on a van transporting immigrants.

– Rick Jervis, Nick Penzenstadler and Lauren Villagran

Who was Joshua Jahn?

Investigators believe Jahn acted alone when he allegedly fired "indiscriminately" at the ICE building earlier this week after a good deal of pre-planning, officials said.

Jahn, a 29-year-old American citizen of Fairview, Texas, about 30 miles from Dallas, didn't appear to belong to any kind of group or entity, Larson said.

Jahn’s older brother, Noah Jahn, told NBC the family grew up in Texas. Joshua Jahn, who was unemployed, was planning to move to Oklahoma with their parents, Noah Jahn told the news outlet. He was registered to vote as an independent, Oklahoma records show.

In 2015, Jahn was charged with delivering marijuana in Collin County, Texas. He eventually pleaded guilty and was issued 5 years of probation and a $500 fine, according to Texas court records.

What happened in the Dallas ICE building shooting?

According to a City of Dallas database of active police calls, 38 police units responded to a 6:38 a.m. call for assistance at 8100 N. Stemmons Freeway, where the local ICE facility is located.

Authorities said a shooter up on a nearby rooftop fired "indiscriminately" at the building and a van holding the detainees in a sally port. Jahn is believed to have accessed the roof using a ladder and was seen driving with a ladder earlier in the morning, officials said.

Three detainees were shot, with one killed and two in critical condition, the Department of Homeland Security said.

While gunfire was still ringing out, ICE and Bureau of Alcohol, Tobacco, Firearms and Explosives officers "ran back into danger... to save the detainees," said Marcos Charles, the ICE executive associate director for enforcement and removal operations.

Contributing: Michael Loria, Eduardo Cuevas and Nick Penzenstadler, USA TODAY

This article originally appeared on USA TODAY: Dallas ICE gunman wrote of spreading 'real terror' to agents, authorities say

Reporting by Jeanine Santucci and Christopher Cann, USA TODAY / USA TODAY

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