LOS ANGELES (CBSLA.com) — All Los Angeles Unified School District students returned to school Wednesday after an email threat that shut down the entire system.

Crisis counselors were on hand to help students feel safe and visible security will be in place among all campuses. Teachers were also provided with lesson plans to help comfort students who may be nervous or anxious.

READ MORE: Los Angeles Clippers Hold Off Lakers, 119-115

Authorities are now saying the email threat was not credible.

School district officials announced the system-wide closure of more than 1,000 campuses around 5 a.m. on Tuesday.

All buses were told to return to the bus yard for the remainder of the day.

City officials checked and cleared each school to determine there was no present threat.

A preliminary investigation revealed the school district received an email threatening to use explosive devices and firearms late Sunday evening.

According to LAPD Chief Charlie Beck, the email was delivered from Frankfurt, Germany. However, the origin of the document is believed to have been sent through a router in the U.S.

The author of the email — who claimed to be a Muslim, former LAUSD student who teamed up with a Jihadist cell — used a device to mask the location of where the email originated.

READ MORE: Gaudreau, Tkachuk Lead Flames Over Ducks In Shootout

(credit: CBS News)

(credit: CBS News)

The email read in part: “We have bombs hidden in backpacks and in lockers at several schools and they are strategically placed to crumble the foundations of the very buildings that monger so much hate.”

Federal officials are now working to locate the person responsible for making the threat in order to determine the motive behind the incident.

Authorities are also investigating whether that person acted alone.

City officials later learned that New York received a similar threat, which was dismissed as a hoax.

NYPD Commissioner Bratton responded to the incident by suggesting L.A. school officials overreacted to the email. This subsequently prompted discussion about the two cities responses.

However, Mayor Eric Garcetti and Beck responded to Bratton stating they respected the superintendent’s decision, saying limited information was available Tuesday morning.

MORE NEWS: La Mirada Home Decorated Like 'National Lampoon's Christmas Vacation' Could Face Fines Over Display

The closure would typically cost LAUSD around $29 million. However, the state superintendent told the Los Angeles Times that he is certain the district will not be docked any fines.