It appears that Ma'an's early story about the death of Hamas co-founder Muhammad Al-Mabhouh being from cancer was not accurate, and he was in fact assassinated. (I was waiting for the UAE police to say something on the matter.)
One Israeli media outlet says it was a Mossad hit. Inyan Merkazi says that Mabhouh was negotiating a deal to transfer arms from Iran to Gaza and was killed by four Mossad hitmen who first interrogated him and got lots of good information.