Hurting/Killing another Muslim when be attacked yourself

I would like to know what the Hukm is on hurting/killing another Muslim. I know that it is one the gravest sins to kill another Muslim, but what if they are attacking you and in order to defend yourself it would mean to seroiusly injure them or kill them ? Not too long ago when I was on holiday in Bangladesh, I was travelling on my own in a taxi and I was hijacked. They beat me up quite badly, but at one point in the taxi, I had the ability to take one of the knives of the attackers. But I didn't, because I didn't know if I was allowed to hurt them or not, so I let go of the knife. Alhamdullillah I recovered from my injuries, but I was told that I was fortunate in that they didn't kill me, as commonly occurs in these cases.
Secondly is it allowed to steal from thieves and robbers in order to protect yourself and the public from harm. For example I had the option of throwing the knife out of the window (at the time it didn't cross my mind), but would that be Haram since it is not my property to dispose of ?

Assalamu alaykum

In the name of Allah the Inspirer of truth.

Islam is a practical religion. It is certainly permissible to defend oneself and ward of one's aggressors. The Prophet sallallahu alayhi wasallam said, "Whoever is killed protecting his wealth is a martyr. Whoever is killed protecting his family is a martyr..." (Ahmed and Tirmidhi). Allama Ibn 'Abidin states:

"If a person is traveling and he came across some dacoits, it is permissible for him to kill them, even if they did not attack him but attacked others, due to relieving the people of their harm" (Radd al-Muhtar 3:180). As such, it would also be permissible to relieve the hijackers of their knives or other weapons and dispose of them.

And Allah knows best.

Wassalam
Abdurrahman Ibn Yusuf