By Todd Quinones

WILMINGTON, Del. (CBS) — The FBI is involved in a $3 million mystery. The largest mined ruby in the world was stolen from a jewelry store in Delaware as part of a massive heist.

“I heard the smash of glass and … I knew we were being robbed,” said jewelry storeowner Jim Stein.

Stein and his son were in the back room eating lunch and hit the silent alarm when four men, three of them masked, stormed into Stuart Kingston Jewelers at 1:30 p.m.

“He (the suspect) had the gun and went to the back over here and tied up two employees,” said Stein.

Jim’s son Edward was forced to open the safe.

“‘Give me the loose diamonds. I want the loose diamonds.’ That’s what’s they kept saying,” Edward Stein said.

Among the loose diamonds was The Liberty Bell Ruby, a four pound, eight and a half thousand carrot ruby sculpted into the Liberty Bell with 50 diamonds on it.

“It’s been appraised at $2 million dollars, it’s irreplaceable. Everything else in the store is replaceable. That’s not replaceable,” Jim Stein said.

Enclosed in a case in the safe, Edward tried to buy time for the police and distract the robbers from noticing the ruby, but they grew impatient.

“The ruby was right there and he swept it into the bag,” said Edward.

After smashing 11 cases and grabbing other diamonds and precious gems, the suspects then took off in a U-Haul rental van before police arrived.

The ruby and the men haven’t been seen since the robbery on November 1st.

No one was seriously injured.

The jewelry store was just holding the ruby for a foundation.

The owners of the stone, which was found in east Africa in the 50’s, were hoping to sell it and donate the money to charity.