Hello everybody

i need your help on this thanks in advance :)

My current situation:

I am foreigner with moroccan cititzenship. For 15 months i have worked in germany
for a company as an engineer. The AT that im currently have is:

Blaue Karte EU
§19a i.v.m. 2 ABS. 2 BeschV

with zusatzblatt:

Erwebstätigkeit nicht gestattet. Gilt nach Par. 39
AufenthG i.V.m. Par. 19a Abs. 2 BeschV nur zur Beschäfitung als
System Engineer bei Fa. XXX. Räumliche Beschränkung: bundesweit.


Now:
I will be changing my job as in 01.01.2018 since i want to pursuit my PHD, I received
an offer letter with this Anmerkungen:

... Wir beantragen eine befristete AE gem. §18 AufenthG.

Da es sich um eine wissenschäffliche Tätigkeit handelt und Sie somit die Argentur für Arbeit nicht
beteiligen müssen, bitten Sie, die befristete Aufenthalterlaubnis nach §5 Nr. 1 BeschV als Akademische/r Mitarbeiter/in
bei der Uni XXX ist erlaubt.


hence i went to the ABH with this letter. And they said that i cant keep by Blaue Karte and since im am morrocan, they said i
cannot start my new job on the 1st January, since they need to background check me for any criminal records. I can start my job
then earliest of mac/ april. It means that i will lose my new job and this will ruin me.

My Question:

1. Is what the lady in the ABH right? Under which § in the AufenhG that stated such neccesitiy to background check me?
2. Can you guys help me on this matter, what type of AT should I beantragt? Any § that i can follow.
3. I need some kind of writting, to explain my situation (better in german) to make sure that the lady in ABH understood what
i need.

Please guys help me since my future depends on this. I have submited my kündigung, and now this  :(