Man Arrested in Girlfriend's Death, Fell Off Cliff After Marriage Proposal

A man in Turkey is in jail, accused of throwing his girlfriend to her death off a clifftop where he had just proposed to her ... and cops think she said, "no" before the fatal tumble.

Nizamettin Gursu has just been arrested in the death of his girlfriend, Yesim Demir, who reportedly fell 100 feet to her death in the Turkish city of Canakkale.

His arrest comes about 5 months after Yesim's fatal fall. Gursu originally told police his GF accepted his proposal, he left her at the edge of the cliff to grab food and drinks from his car and then heard her scream. He said he returned to find she had fallen over the ledge.

However, cops say their investigation now leads them to believe Yesim rejected the proposal, and a struggle ensued at the scenic picnic spot ... a struggle that ended with her going over the cliff to her death.

Police say Gursu still had the engagement ring in a box in his pocket ... and they also found a broken speaker and shattered glasses where the July 6 proposal went down.

What's more, cops say Yesim's family told them she had been planning to break up with Gursu before the proposal ... and they say she would have never gotten engaged to him.

The woman's family also told police she would not willingly stand at the edge of a cliff because she suffers from panic attacks.