Were Iran and Hezbollah involved in 9/11?

According to a Ynet article, the 9/11 commission knew some of the evidence led in the direction of Iranian involvement and failed to follow the lead:

[...] At the end of the day, the commission noted in its report that the issue deserves further scrutiny by the US Administration. However, such examination was not undertaken and may have never materialized. Indeed, this entire affair may have remained buried in the three abovementioned pages, had it not been for one brave woman: Ellen Saracini.

Saracini is not an intelligence analyst or counter-terrorism expert. She is the widow of pilot victor Saracini, the captain of the Boeing jet that took off from Boston aboard United flight 175, which was crashed into the southern tower. However, Ellen was unwilling to see the death of her husband and father of her two daughters end with yet another line in the commission’s report; she decided to seek justice on her own.

Saracini approached attorney Thomas Mellon, who specializes in lawsuits against large corporations. Mellon’s team members launched an investigation. They met potential witnesses, interviewed intelligence officials, CIA agents, Iranian defectors, a French judge and others. They even reached Israel in their search (in the interest of full disclosure, the writer of this article was also summoned to testify in the trial, as one of nine expert witnesses.)

The investigation kept progressing, diving deep into the dark corners of the global world of intelligence and terrorism. Ten years later, Mellon and his team are convinced that they possess the “smoking gun” that will tie Iran to the September 11 attacks. [...]

See the original for most of the substance of the article. (h/t: Israel Matzav)