why does my object reappear in the same spot after using self.kill()?

So i am quite new at pygame. im creating a game about shooting the alien using a spaceship. So the spaceship will keep on shooting bullets and we have to move the spaceship around so the bullet will hit the alien and the alien will die after getting hit 5 times. The alien will keep on coming down and move left and right to make the game harder. So i tried to kill the alien by using the self.kill() but after it dissapear, it reappear again at the same spot. Why is this happening and how do i fix it?

import pygame

shoot_timer = pygame.USEREVENT + 1
pygame.time.set_timer(shoot_timer,400)
enemy_timer = pygame.USEREVENT + 2
pygame.time.set_timer(enemy_timer,4000)

class Enemy(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        alien = pygame.transform.rotozoom(pygame.image.load(os.path.join('Assets','enemy.png')).convert_alpha(), 1, 0.8)
        self.image = alien
        self.rect = self.image.get_rect(bottomleft=(randint(0, width - self.image.get_width()), randint(-200, -150)))
        self.lives = 5
        self.movement_index = 0
        self.movement_place = [-2,2]
        self.movement_a = self.movement_place[self.movement_index]
    def movement(self):
        self.rect.y += 1
        self.movement_index += 0.005
        if self.movement_index > len(self.movement_place):
            self.movement_index = 0
        self.movement_a = self.movement_place[int(self.movement_index)]
        self.rect.x += self.movement_a
    def destroy(self):
        if self.lives <= 0:
            self.kill()
    def update(self):
        self.movement()
        self.destroy()

class Spaceship(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        red_spaceship = pygame.image.load(os.path.join('Assets', 'spaceship_red.png')).convert_alpha()
        red_spaceship = pygame.transform.rotozoom(red_spaceship,180, 0.15)
        self.image = red_spaceship
        self.rect = self.image.get_rect(midbottom=(width//2,height-20))
        self.bullets = []
    def shoot(self):
        bullet_rect = pygame.Rect(self.rect.x + self.image.get_width()//2 -1, self.rect.y - 5, 3, 15)
        self.bullets.append(bullet_rect)
    def player_input(self):
        key = pygame.key.get_pressed()
        speed = 5
        if key[pygame.K_w] and self.rect.top > 60:
            self.rect.y -= speed
        if key[pygame.K_s] and self.rect.bottom < height:
            self.rect.y += speed
        if key[pygame.K_a] and self.rect.left > 0:
            self.rect.x -= speed
        if key[pygame.K_d] and self.rect.right < width:
            self.rect.x += speed
    def update(self, a):
        if a == '':
            self.player_input()
            for bullet in self.bullets:
                bullet.y -= 10
                pygame.draw.rect(screen, yellow, bullet)
                if bullet.bottom < -10:
                    self.bullets.remove(bullet)
                if enemy.rect.colliderect(bullet):
                    self.bullets.remove(bullet)
                    enemy.lives -= 1
        else:
            self.shoot()

enemy = Enemy()
enemy_group = pygame.sprite.GroupSingle()
spaceship = Spaceship()
spaceship_group = pygame.sprite.GroupSingle()
spaceship_group.add(spaceship)

def draw_surface():
    spaceship_group.draw(screen)
    spaceship_group.update('')
    enemy_group.draw(screen)
    enemy_group.update()

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            exit()
            if event.type == shoot_timer:
                spaceship_group.update('a')
            if event.type == enemy_timer:
                enemy_group.add(enemy)

    draw_surface()

    pygame.display.update()
    clock.tick(60)