If your son has a fresh bite mark on his shoulder, enough so that the police have taken impressions of your teeth to try to rule you out/in for it, then I'm afraid I CAN understand their decision to place him in FC.
I was rather chaotic and didn't keep good company when I was young and first had my DD. I realised that it was down to me to decide what sort of people had access to my child/ren, and I cut myself off from my old circle of friends, and started making new ones from toddler groups, sing along sessions etc, and I chose my friends very carefully.
Nowadays, I look back, and I am glad I had the wake up call of my DD being in FC for two weeks, because although it was the worst feeling in the world, it gave me the impetus to change my life, and more importantly, that of my DD.
She is now 14yo, has lived with me ever since, and I have had no major SS involvement since she was 4yo.
You REALLY need to think hard about the company you keep, because while YOU choose who you spend time with, your child has no choice in that. So you need to choose very carefully, and make your choices with your child in mind first, THEN who you would like to see second.
I hope you resolve this, but like me, it will take a complete lifestyle overhaul, engagement with all services offered, and doing everything with your son's well being in mind first and foremost.
It IS a good sign that you have been allowed contact for 5 days a week rather than the standard 2. They usually do that in cases where they can see the resolution in the longer term of the child being reunited with their parent, provided the parent makes the necessary changes to their lifestyle.
You have my best wishes, and I hope you can engage with the services offered.