Did local plumber catch wind of Istanbul attack plot?

New details on Istanbul killers' days before attack

ISTANBUL -- A second-floor apartment in a working class Istanbul neighborhood is where the suicide bombers are believed to have lived in the weeks before the devastating attack on Turkey's bustling international Ataturk Airport.

Turkish police raided the apartment the morning after the massacre, but one local resident tells CBS News correspondent Holly Williams he visited the apartment before the attack, and may have smelled the explosives used by the bombers.

What was intel before Istanbul airport attack?

New security camera video shows the terror in the departures area in the Ataturk terminal as one of the attackers, armed with a gun and suicide bomb, went looking for victims.

One of the suicide bombers is thought to have been a Russian citizen from the north caucuses region, the two others from Uzbekistan and Kyrgyzstan.

It's estimated that several thousand fighters from Russia and former Soviet republics have joined the Islamic State of Iraq and Syria (ISIS), which is believed to be the most likely culprit behind the attack.

The Istanbul neighborhood where the attackers apparently holed-up is popular with people traveling to and from Syria.

Erdal Simsek is a local plumber, and he told CBS News that when one of the men asked him to fix a leaking tap just a few days ago, he noticed a strange odor in the apartment.

"I asked the man what it was, but he just waved me away," said Simsek.

New details in Istanbul terror attack probe

Explosives experts believe it could have been a chemical precursor used in the suicide vests.

Turkish media and one U.S. official have named Akhmed Chatayev, an ISIS commander from Chechnya, as the suspected organizer of the massacre, but so far there's been no official confirmation of that.

Turkey's been accused in the past of not doing enough to stop foreign fighters from passing through its territory to reach ISIS in Syria. It now seems that some of those foreign fighters may have targeted Turkey and its biggest airport.