Merseyside Police dog Ghost was searching for offenders who had entered premises in Southworth Road in St Helens yesterday early morning.
Police said the three-year-old German shepherd was found shortly afterwards on the M6 nearby with traumatic injuries after being hit by a vehicle.
His handler Police Constable Dave Bartley was extremely upset over the incident, the BBC reported.
Police said no vehicles stopped at the scene where Ghost was found.
Ghost had been a serving police dog for most of his three years and worked on numerous jobs.
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Inspector Tony Byrne said he feared Ghost would have to be retired after suffering a lot of damage to his tail and a torsion in his stomach last year.
"It is rare for dogs to recover from things like this but he was big strong dog and came back from it."
He added: "Ghost and his handler were a prolific team and he was a much valued member of our team and will be sorely missed.