How can I take Sarah's personal effects?

Hint 1 of 8:

You will need permission from someone at Scotland Yard.

Hint 2 of 8:

Gregson can't give you permission, but he'll tell you who can.

Hint 3 of 8:

If you need help getting into the Yard, see a later question.

Hint 4 of 8:

Now all you need to do is contact Lestrade.  A bit of inside help is needed.

Hint 5 of 8:

Have you talked to the blind man outside?