Image copyright AP Image caption Adnan Syed was sentenced to life plus 30 years for killing his ex-girlfriend

The lawyer of Adnan Syed, the subject of the hit US podcast Serial, has submitted new evidence that he says casts doubt on his client's conviction.

Justin Brown says key mobile phone data used to convict Syed of killing his ex-girlfriend in 2000 was unreliable.

Syed, 35, is serving a life sentence for the murder of Hae Min Lee in 1999.

His defence team is trying to reopen the case based on some of the questions raised in the Serial podcast over whether Syed had received a fair trial.

Serial, which was released in weekly instalments at the end of last year, became a global hit, breaking records as the fastest podcast to reach five million downloads on iTunes.

'Incoming calls not reliable'

In the 2000 trial, prosecutors weighed heavily on mobile phone records that allegedly placed Syed at a park in Baltimore where Lee's body was buried. Syed, who was 17 at the time, has always maintained his innocence.

But a motion filed in court on Monday by Mr Brown said a newly recovered mobile phone document showed "the cell tower evidence was misleading and should have never been admitted at trial".

In it, Mr Brown says mobile phone carrier AT&T had issued a warning about the accuracy of mobile tower data, which he argues would have made the phone records inadmissible as evidence.

"Outgoing calls only are reliable for location status. Any incoming calls will NOT be considered reliable information for location," reads a note on a cover sheet from AT&T for Syed's phone records.

Image copyright Serial Podcast Image caption Serial was one of the most popular podcasts of all time

But Mr Brown says prosecutors presented incoming calls as evidence to determine Syed's location.

It "is an extremely important piece of evidence, and we are bringing it to the court's attention as quickly as possible," Mr Brown told The Baltimore Sun.

Syed's lawyer is also seeking to reopen court proceedings to allow testimony from a key witness who may be able to provide Syed with an alibi in the case.

Asia McClain, a friend of Syed's who was not heard in the original trial, claims to have seen him in a library at the time of the suspected killing.

The fact that Syed's first lawyer, Cristina Gutierrez, failed to submit this evidence in the original trial was one of the arguments used to win him the right to appeal in February.

Syed's lawyer has since filed a motion for appeal, though the court in Maryland has yet to respond.