Why did Viktor wait so long to kill Selene's family?

Question

In the Underworld series, Viktor commissions a Master stonemason and Metalsmith to design, excavate and build a dungeon underneath Viktor's fortress. Unbeknownst to the stonemason, this would later become William's prison.

Viktor wanted to eliminate all evidence regarding the building of the prison and decided to kill the stonemason and his family so that nobody could ever be persuaded to tell Lucian or William of the whereabouts of the prison.

Viktor was so obsessively afraid of Marcus finding out where his brother was hidden that he even lied to the men who helped him in executing the families of the dungeon's builders, telling them he was merely in need of blood. Viktor tracked down the head builder and slaughtered his family with the aid of Soren and Kraven.

It is revealed that the stonemason is Selene's father and construction started on the prison when Selene was approximately 6-7 years old. Viktor kills Selene's family and turns Selene into a vampire when she was 19 years old.

If Viktor was so worried about anyone finding out about the whereabouts of the prison, why did he wait so long to kill Selene's family after construction was complete? Or, did construction on the prison just take a long time causing construction to continue for approximately 12-13 years?

Answer 1

Yet again we have to look at the murky dates and sequel decay for the answer.

1. The Werewolf prime, William is captured in 1202 AD.
2. Lucian the first Lycan is born in 1207 AD.
3. Selene is born, 1383 AD.
4. Williams prison is under construction, Selene 7ish, 1390 AD.
5. Prison is complete, one key is given to Sonja.
6. 195 years of Lycan slavery and a Romeo and Juliet story come to a head. 1403 AD.
7. Main Events of Rise of the Lycans happens.
8. Selene is turned at 19 years old, 5th Century, 1403 AD.

If we fudge these numbers around a bit, it's easy enough to piece together. Viktor was motivated into keeping the secret hidden from Lucian, who just initiated the first strike of the Vampire-Lycan war. His numbers have been diminished by the attack, and while he could manage Marcus, Lucian's army is another story. He didn't need to kill the builders until after Rise happens.