Angular 2 attr.disabled not behaving as expected

I have a list of items to display and alongside each item there is a checkbox. I have a condition statement to check whether each item's checkbox should be disabled or enabled. For some unclear reason every checkbox in my list is disabled and i am not sure if it is how i set up the [attr.disabled] or an error in my condition statement.

Here is my html:

 <input class="form-control" [attr.disabled]="disabled == true ? true : null"
     type="checkbox"[checked]="item.status" (click)="itemChecked($event, item)" />

In my component:

private disabled: boolean;

for( let item of items){
if (item.id == Status.required) {
                item.status = true;
                this.disabled= true;
            } else if (item.id != Status.required && item.list.length > 0) {
                item.status = item.id == Status.checked
                this.disabled= false;
            } else {
                item.status = item.id == Status.unchecked;
                this.disabled= false;
            }
    }

Currently in my list regardless of the status of my item, all check boxes are disabled and not sure why.