DALLAS -- Dallas City Marshals were among the officials investigating after hundreds of pieces of mail were dumped into a southern Dallas creek bed.

Authorities gathered the mail from Cedar Creek in Dallas’ Wynnewood North area, and placed it into large evidence bags for processing. Marshals were investigating it as an illegal dumping case.

Postal police and investigators from the USPS Office of Inspector General were looking into whether any federal laws had been broken.

"This wasn't an accident," said Dep. Chief Paul Hansen, Dallas City Marshals Office. "It wasn't something that blew out of a truck or something like that, it was purposefully dumped in the creek."

"It's very rare," Hansen added. "I've never seen this [amount] of mail dumped before."

Dallas Marshals investigate a large pile of mail that was dumped into Cedar Creek in southern Dallas early Tuesday morning.

They have identified the employee involved in the incident, according to Jeff Krafels, U.S. Postal Service Office of Inspector General (USPS OIG) Assistant Special Agent. It was a city carrier assistant who officials say is no longer employed with the U.S. Postal Service.

A neighbor told WFAA he saw a mail truck parked across the street from his home in the 500 block of Manus Drive around 5:15 p.m. As he was blowing leaves from his driveway into the creek, he noticed some mail on the ground, and went to pick it up, thinking it was litter.

That’s when he saw the pile of mail in the Cedar Creek bed.

“First, I thought maybe someone had stolen some mail and threw it [into the creek]. But when I saw hundreds of pieces of mail, I knew it wasn’t that,” said Don Sutton. “Then I thought maybe [the mailman] spilled a tub or something. But no, this had been thrown down there.”

A large pile of mail was dumped into Cedar Creek in southern Dallas early Tuesday morning.

The mail would be processed as criminal evidence, including possibly trying to life fingerprints, officials said, before being delivered to the people for whom it was meant.

Addresses listed on the mail were for homes in the 75224 zip code, the same area where it was dumped, said Sutton.