Gunmen kill third top Mexican policeman
Assailants sprayed the car of the deputy police chief of the border city of Ciudad Juarez on Saturday, killing Juan Antonio Roman Garcia.
The head of Mexico City's anti-kidnap unit was killed on Friday.
On Thursday, the director of national police operations against drug traffickers was shot dead.
Speaking before the latest killing, Mexican President Felipe Calderon said such attacks would not deter his efforts to continue his government's campaign against drug-trafficking cartels.
"We have to come together to confront this evil, we Mexicans have to definitively and categorically say 'That's enough!'," he said at a police memorial service.
"We can't accept this situation. We have to take back our streets."
'City in mourning'
Mr Garcia was shot dead outside his home in Ciudad Juarez, which borders Texas.
President Calderon was at a memorial to dead police officers this week
His name had appeared at the top of a "hit list" left at a monument for fallen police officers a few months earlier.
"His death has plunged the city into mourning because he was an exemplary officer with an impeccable 20-year record who fulfilled his duties until his last breath, despite the dangers," said the city's mayor, Jose Reyes Ferriz.
All police officers have been ordered to take added precautions, he added.