The Testament of Sherlock Holmes

I am in the final section of the chapter called whitechapel. Sherlock and Dr. Watson have gotten out of the storage room in the opium den and Dr. watson is distracting the guard.

I have tried for hours to tranquilize the guard but cannot get the green symble of the hypodermic needle to appear as he walks past the corner of the hallway.

I am playing the PC windows version and wonder if this is a know problem?

Has anyone found an easy way to accomplish this symple but otherwise impossible for me to complete.

I have watched a video on this paricular event and it looks so simple but is probably being done on xbox or PS3.

That's interesting. Please check the label of the hypo in inventory to see if it is - syringe with soporific. If it is not - then the syringe does not contain the correct substance.
Also did Holmes talk to Watson about distracting the goon?
Keep us posted.