December 27, 2016 11:00 AM

They have been on the hunt since mid-March, but investigators in Phoenix, Arizona, tell PEOPLE they are no closer to apprehending the suspected serial killer believed responsible for fatally shooting at least seven people and injuring three more.

Phoenix police spokesman Jonathan Howard says “there are currently no active, specific, [or] credible leads,” but investigators continue to follow up on “every lead that we encounter.”

Police believe all of the shootings were carried out at random. They say the killer’s crime spree began on March 17, when a 16-year-old boy was shot and injured as he walked down a street.

A police sketch of a suspected serial killer in Phoenix, Arizona.
City of Phoenix Police Department

The youngest victim is 12-year-old Maleah Ellis, who was killed on June 12 with her mom, Stefanie Ellis, and family friend Angela Linner.

All three were shot as they sat in a car listening to music outside their Maryvale home in Phoenix, according to police. Investigators say the shooter pulled up alongside the car and opened fire, hitting the victims more than 30 times.

Maleah’s uncle, Ellis’ brother, described the little girl as “the life of the family.”

“She wanted to have fun all the time. She was just a good girl,” Sylvester Ellis told PEOPLE in July. “She was very, very friendly. Everybody loved her. All the kids in the neighborhood loved her. Lea-Lea was a good girl.”

Of his little sister, Sylvester said, “[Stefanie] was a mother and a father to her kids. She was a single parent to her kids. … She was everything to us.”

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Maleah Ellis (left) with mom Stefanie Ellis
Sylvester Ellis

Other murder victims believed to be connected to the killer include Diego Verdugo-Sanchez and Krystal White, who were both gunned down in April; and Horacio De Jesus Peña and Manuel Castro Garcia, who were fatally shot in June.

The last shooting occurred on July 11, when someone opened fire on a 21-year-old man and a 4-year-old boy as they were sitting in a car, according to Phoenix police. The man and boy were not injured in the shooting and have not been identified.

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“Unfortunately, there are no significant updates,” Howard tells PEOPLE. “The last strike was July 11, 2016. No additional incidents have been identified as related since that time. Our investigators continue to work, but there have been no significant updates in the last several months.”

The shooter is described as a thin man in his 20s. Police have asked that anyone who may have any information about the shootings come forward.

Authorities are offering a $50,000 reward for any tips that lead to an arrest — more than double the $20,000 originally offered.

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