KANSAS CITY, Mo. -- A reward in the case of a man shot and killed on the job while taking a smoke break has increased to $6,000.

Napoleon Malone, 26, was on the phone with his mother on May 7 just outside the Renaissance West rehabilitation center in Kansas City where he worked when a group of people approached him and he was shot.

When officers arrived at the facility, they found Malone dead on the sidewalk.

"He called me because he was upset, standing outside his job," Paula Malone said the following day. "Everyone said there were four people who walked up. I had to hear my son scream and hear the people yell profanity. This man has done nothing to nobody."

Malone worked the overnight shift there and was studying to become a substance abuse counselor.

Catherine Ford was his supervisor.

"It's kind of rough to look at his picture, because it was very senseless, very unnecessary," Ford said.

She hoped that anyone who knew who killed him would come forward, Ford said.

Their employer added $5,000 to the existing $1,000 Crime Stoppers TIPS Hotline reward.

"It's the very least we can do to honor someone and more than honor someone. There needs to be some closure. We really need to get these individuals off the street, because this was random, which means they can do it to somebody else anytime," said Bill Kyles, the president of the company.

Kyles said the company had increased security at the center. They hired an off-duty police officer to work during the overnight shift that Malone worked, 11 p.m. to 7 a.m.

Authorities encouraged anyone with any information in the case to call the TIPS Hotline at 816-474-TIPS.