MIAMI (CBS4) – South Florida postal workers can breathe a sigh of relief after learning three arrests have been made in connection with a recent string of postal worker robberies that officials now say are unrelated.

Three female letter carriers were robbed, sometimes at gunpoint, in the last month. Each time, the suspects took their master mail keys which give the bad guys access to locked mail boxes.

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After thousands of man hours spent investigating the robberies, the U.S. Postal Inspector in Charge announced details about the arrests on Wednesday morning.

“Last year in South Florida, I should say in the entire state of Florida, we had three robberies,” said U.S. Postal Inspector in Charge Henry Gutierrez.

Gutierrez it was hard work that led to the arrest.

“This is a great testament to the great law enforcement community and the interaction we have in our community to solve our problems,” said Gutierrez.

Using tips from the community, two teenagers were arrested along with 18-year-old Steven Daniels. All have been charged with robbery with a weapon. Daniels appeared in bond court Wednesday where the judge ordered him to be held on $100,000 bond.

Daniels and one of the teens were arrested in connection with beating and robbing a letter carrier on October 7th in Miami Gardens. The second teen was arrested for robbing a carrier at gunpoint outside an apartment building October 17th on NE 6th Avenue. The third incident remains unsolved.

At his home in Opa Locka, Daniel’s mother Cathy Cook told CBS4, “He’s never been mean or violent to me.  He’s very respectful with me.  He takes care of his daughter.  No one here can believe it.”

Cook said her son was going to school to get his GED and that he’s a proud brand new dad.  While she has yet to able speak to him about what happened she said, “If he is the person there is nothing to do but to own up to it. That’s the only thing to do.”

While all three crimes took place in the northern part of Miami-Dade, investigators don’t believe the thieves were conspiring. But they were alarmed when they suddenly had three in one month.

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“It is not necessarily a ring. We haven’t found any connection between one group or the other,” said Gutierrez.

With more than a quarter million mail carriers on the road nationwide, theft of master mail keys is extremely rare.

“In the whole spectrum in what I just told you we have less than 100 robberies total. And that’s facilities, truck drivers, and letter carriers. Last year in South Florida, I should say in the entire state of Florida we had three robberies,” said Gutierrez.

Detectives spent thousands of hours following up tips.  The robbers were targeting female carriers in the northern part of Miami Dade.  While the thieves were all after mail keys that opened up locked mailboxes, investigators say the robberies don’t appear to be connected.

“It is not necessarily a ring.  We haven’t found any connection between one group or the other.”  Gutierrez said.

Following the recent crimes, the postal service has taken steps to eliminate their master mail keys as a target.

“We are changing our system. We are in the process of changing the system and the way we lock these boxes throughout the country and South Florida is in the process of doing that right now,” explained Gutierrez.

The postal service wouldn’t divulge what the exact changes are but they hope their letter carriers will be safer now.

“So those of you that think this is a very good idea, you will be investigated. We’ve shown that with these arrests the past several days. And we are showing you that we are doing something to prevent this from reoccurring,” stated Gutierrez.

There is still one robbery unsolved from October 14th. It happened at 10th Avenue and 146th Street in North Miami.

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There is a $5,000 reward being offered for tips that help solve that case. Anyone with information should call (877) 876-2455 then hit option #2.